Ultra-Violet and Electron Beam Irradiation as an Effective Approach for Design of Ln(III) and Am(III) MOFs

Abstract

The ultraviolet (UV) irradiation for synthesis of the metal-organic frameworks (MOFs) has been applied for the first time. The use of UV radiation enabled the efficient synthesis of 2D-Ln-BTB and Am-MIL-103 MOFs. A comparative analysis was carried out to assess the viability of radiation-chemical and photochemical approaches for the synthesis of Ln(III)- and Am(III)-BTB MOFs. The yields from both methods for all lanthanides reached 90% depending on the cation. The obtained materials were characterized by PXRD, FTIR, SEM-EDX, CHN-analysis, as well as TGA. For a novel Am-MIL-103, the crystal structure was determined using SCXRD and compared with the previously known Ln-MIL-103 analogues. Solvent electron density removal revealed a void space of approximately 4311 Å3 (49.2% of the total unit cell volume), which is smaller than that in the lanthanum analogue (52.3%) due smaller ionic radius of Am. It was demonstrated that a decrease in dose rate from 180 to 8.4 Gy/s results in a significant increase in the crystallinity of the material. In contrast to the photochemical method, the radiation-chemical approach yields only one type of Ln-BTB MOF. This study shows that by varying the conditions of the photochemical synthesis, it is possible to obtain three types of Ln-BTB MOFs with different structures.